Wire sawing devices of the mentioned type, with movement of the wires of the layer of wire or of the piece to be sawed, are already known, especially in the industry of electronic components of ferrites, quartz and silica, to obtain thin slices of material such as poly- or monocrystalline silicon or new materials such as GaAs, InP, GGG or else quartz, synthetic sapphire, ceramic materials.
In known devices, the sawing region is constituted by the assembly of at least two cylinders disposed parallel to each other. These cylinders, called wire guides, are engraved with grooves defining the interval between the wires of the layer, thus the thickness of the slices. The piece to be sawed is fixed on a support table which moves perpendicularly to the layer of wires. The speed of movement defines the cutting speed. Replenishment of the wire, as well as control of its tension, is carried out in a portion called the management zone of the wire located beyond the sawing region properly so called. The agent which effects cutting is either an abrasive fixed on the wire, or a free abrasive supplied in the form of a slurry. The wire acts only as the carrier. During cutting of the piece to be sawed into thin slices, the stretched wire is both guided and tractioned by the wire guide cylinders. The pieces to be sawed in most cases have a prismatic shape based on a rectangle, a square or a pseudo-square.
In conventional sawing processes and devices, the piece or pieces to be sawed are mounted on the machine such that one of their prismatic surfaces will be parallel to the working plane. During the start of sawing, it has thus been noted that the wires of the layer of wires slide on the surface and have the tendency to group themselves two by two, which gives rise to sawed slices or wafers of unequal thickness (FIG. 10), which is very troublesome for numerous applications, leading to frequent rejection.
During sawing, the layer of wires forms a depression and incurvation due to the force of application of the pieces to be sawed, shown in FIG. 1. At the end of sawing, the wires encounter the intermediate plate, typically of glass, but also of epoxy, graphite or other hard materials, on which the piece to be sawed is cemented. Given their incurvation and inclination, the wires penetrate, during their longitudinal advance from this intermediate plate and from the cement, with a small angle, into the material of the piece to be sawed.
The upper edge of the sawed slices thus undergoes prejudicial chipping which should be avoided in the case of numerous applications.